D3o9 macroporous weakly basic anion exchange resin was used to recover tungsten from the hydrochloric acid leaching solution of scheelite containing arsenotungstic heteropoly acid and transform it into ammonium tungstate solution.The adsorption isotherm,adsorption kinetics,and process conditions of adsorption and desorption of[AsW₁₂O₄₀]^3-by D309 resin were investigated.The results show that the adsorption process of[AsW₁₂O₄₀]^3-by D309 resin fits Langmuir isothermal equation and is monolayer adsorption.The control step of the adsorption process is particle diffusion.Under the optimal conditions of temperature of 55 C,reaction time of 1 h and liquid-solid ratio of 2.5:1,the adsorption rate of tungsten can reach 99.90%.Under the optimal conditions of temperature of 55 C,reaction time of 3 h,ammonia concentration of 210 g/L and liquid-solid ratio of 1.25:1,the desorption rate of tungsten is 91.78%.

The sodium tungstate solution obtained from low-grade scheelite by collaborative leaching with sodium phosphate-sodium hydroxide-calcium fluoride contains a relatively high concentration of fluorine,leading to the fluorine content in the smelting wastewater exceeding the national discharge standard.Based on the low solubility of lanthanum fluoride,lanthanum chloride was added to the sodium tungstate solution and the reaction produced lanthanum fluoride precipitate to thoroughly remove fluorine.The effects of process parameters including the lanthanum chloride dosage,pH value of the solution,reaction temperature,and reaction time on the removal of fluoride were investigated.The results show that the fluorine removal rate reaches 98.8%when fluorine concentration of the sodium tungstate solution is 0.5~2.1 g/L,the dosage of lanthanum chloride is 1.6 times the theoretical amount,the pH value of the solution is 1o.1,the temperature is 60 C,and the reaction time is 30 min,with a tungsten loss of 0.26%in the precipitated slag.After the removal of fluorine,the sodium tungstate solution treated by an ion exchange process can meet the requirement of the national standard for the fluorine content in the discharging wastewater.

Ammonium heptamolybdate was prepared by water dissolving-evaporation concentration removal of ammonia-cooling crystallization method using ammonium dimolybdate as raw material.The effects of concentration degree on crystallization product were investigated,and the effects of concentrated liquid density,cooling rate,crystal growing time,and stirring rate on the particle size and morphology of ammonium heptamolybdate were also studied.The results show that ammonium heptamolybdate crystals with a single phase can be prepared by the evaporation concentration-cooling crystallization method after the water dissolution of ammonium dimolybdate.With a concentrated liquid density of about 1.38 g/cm³,a cooling rate of 30℃/h,a crystal growing time of 1 h,a stirring rate of 150 r/min,and a final cooling temperature of 22℃,the crystals of ammonium heptamolybdate are complete in morphology and prismatic with an average particle size of 337.649μm in a controlled cooling crystallization process.

Rare earth molten salt electrolytic slag is a rare-earth-based solid waste generated during the preparation of rare earth metals and their alloys by molten salt electrolysis,containing abundant rare earth metals,fluorine,and lithium resources.This paper reviews the present situation of valuable metal recovery and reuse from rare earth molten salt electrolytic slag,and introduces the technical advantages and problems of physical,acid,and alkali processes.The paper also focuses on the existing issues and future development trends of industrialized technologies of concentrated sulfuric acid roasting and sodium hydroxide roasting,hoping to provide reference for resource recycling of rare earth molten salt electrolytic slag.

In view of the characteristics and actuality of unbalanced utilization of Bayan Obo niobium concentrate,the electromagnetic action is introduced to realize the dual objectives of efficient separation of metallic iron resources and comprehensive utilization of niobium carbide in Bayan Obo niobium concentrate.In this research,the effect of electromagnetic action on the melting and separation of the niobium concentrate was studied by using self-designed electromagnetic melting and separation device.The results indicate that the electromagnetic action can promote the separation of slag and iron after the reduction of niobium concentrate to reduce the residual iron in the slag.When the current frequency is fixed,the yield of metallic iron increases significantly with the increase of the current intensity.When the current intensity is fixed,the iron yield decreases with the increase of the current frequency.The electromagnetic action promotes the contact between niobium carbide and iron.Under the same current frequency,the content of niobium carbide in iron increases significantly with the increase of the current intensity,while it decreases obviously with the increase of the current frequency under the same current intensity.The magnetic field produced by low frequency and high intensity current can improve the dispersion effect of niobium carbide in iron phase,and the niobium carbide particles in iron are obviously dispersed.

WC-Al₂O₃composite was prepared by vacuum hot-pressing sintering method.The corrosion behavior of the WC-Al₂O₃composite in NaCl solution with different concentrations was studied by electrochemical corrosion method,the open circuit potential,polarization curve and impedance spectrum were mainly mea-sured,and the corrosion surface of the sample was characterized by SEM and XPS.The results show that the corrosion mechanism of the WC-Al₂O₃composite in NaCl solution is the oxidation of WC phase and the dissolution of Al₂O₃phase.With the increase of NaCl solution concentration,the corrosion current density decreases from 19.2μA/cm²to 7.5μA/cm²,while the total impedance increases from 178702·cm²to 215342·cm²,gradually improving the corrosion resistance of WC-Al₂O₃.When the NaCl solution concentration is high,the decrease of dissolved oxygen content in the solution becomes the main factor to control the electrochemical corrosion.The low dissolved oxygen content inhibits the electrochemical reaction process of the cathode,thereby inhibiting the overall electrochemical corrosion rate.

Due to its excellent physicochemical properties of high strength at high temperature,good corrosion resistance,and strong radiation resistance,molybdenum coating has promising application prospects in metallurgy,aerospace,and nuclear industry.This paper reviews the main preparation methods of the molybdenum coating,including thermal spraying,physical vapor deposition and electrodeposition,and compares the advantages and disadvantages of different methods.In addition,the research status of the electrodeposition of the molybdenum coating in molten salt and aqueous solution is emphasized.The comparisons of the effects of active salt,support electrolyte,and additives on molten salt electrodeposition and molybdenum coating quality are also conducted.At present,the molybdenum coating prepared in molybdate-fluoride-oxide molten salt system has the best comprehensive performance.Aqueous solution electrodeposition has low preparation temperature and wide applicability,but it faces the difficulty of restraining hydrogen evolution and the problem of MoO₄^2-being sensitive to pH value,resulting in weak bonding between the molybdenum coating and the interface.

The effects of the combined addition of Sc and Zr on the microstructure and mechanical properties of ZL114A alloy were studied by polarized light microscope,DSC,SEM and Vickers hardness tester.The results show that for ZLll4A alloy with Al-Ti-B grain refinement,the nucleation temperature of primaryα-Al grains increases from 619.2 C to 621.6 C after the combined addition of Sc and Zr,and the number of nucleation cores also increases.The nucleation ofα-Al grains becomes easier and the grains are further refined,of which the size decreases by 9.8%from 319.2μm to 287.8μm.The combined addition of Sc and Zr has little effect on the eutectic Si of ZLll4A alloy,indicating that the change in mechanical properties of ZLl14A+Sc+Zr alloy is mainly attributed to the change in the size of primaryα-Al grains.After the combined addition of Sc and Zr,the hardness of ZL1l4A alloy increases due to grain refinement.

GCrl5 bearing steel with different Y contents was prepared by vacuum induction furnace,and the effects of rare earth Y on the fatigue and wear resistance of the GCrl5 bearing steel were investigated by bending fatigue test and sliding wear test.The results show that the fatigue life of the test steel significantly increases with the addition of the rare earth Y.The fatigue fracture morphology of the test steel without Y addition is mainly fluvial and slightly dimpled,and the fracture mode is brittle fracture.The fatigue fracture of the test steel added with a small amount of Y exhibits fatigue striations,and its width decreases with the increase of rare earth Y.In addition,the fatigue fracture inclusions of the test steel without Y addition are MnS-Al₂O₃ composite inclusions with irregular angles,which are modified into spherical Al-O-Y-Mn-S rare earth inclusions with the addition of a small amount of Y,thereby improving the fatigue performance of the test steel.With the increase of rare earth Y,the wear loss of the test steel gradually decreases,its friction coefficient gradually decreases as well,and the wear resistance is enhanced.The wear mechanism of the test steel is a joint action of abrasive wear and fatigue wear,and with the increase of rare earth Y,the abrasive wear and fatigue wear gradually reduce.

Bayan Obo rare earth tailings are composed of hematite,bastnasite,fluorite,quartz and magnetite,in which rare earth element Ce and transition metals Fe,Mn are the active elements required for catalyst.In this paper,activated rare earth tailings were modified by Ce using impregnation method,and the effects of Ce modification on the performance of activated rare earth tailings catalyst were investigated by SEM-EDS,XRD,BET,NH₃-TPD,H₂-TPR and XPS.The results show that the Ce-modified activated rare earth tailings catalyst is dominated by mesoporous structure and Ce element is highly dispersed on the catalyst surface.There is a synergistic effect between Ce and Fe,and the existence of a redox couple between them promotes the transformation between different valence states of Ce and Fe ions,enhances the redox ability of the catalyst and increases the number of acid sites,which provides favorable environment for the adsorption and activation of NH₃,improving the denitration efficiency of the catalyst.After being modified by 15%Ce,the denitration efficiency of the activated rare earth tailings increases from 70%to 82%,the N₂selectivity is above 90%,and the reaction temperature window is widened to 275~450℃.